1. Field of the Invention
The present invention relates to a method and apparatus for facilitating RRC connection between a terminal and UTRAN in a UMTS (Universal Mobile Telecommunication System) and, more particularly, a method and apparatus for facilitating RRC group reject through which the UTRAN may perform RRC connection reject using a single message transmitted to a plurality of terminals.
2. Description of the Related Art
A universal mobile telecommunication system (UMTS) is a European-type, third generation IMT-2000 mobile communication system that has evolved from a European standard known as Global System for Mobile communications (GSM). UMTS is intended to provide an improved mobile communication service based upon a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology.
In December 1998, a Third Generation Partnership Project (3GPP) was formed by the ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, and the TTA of Korea. The 3GPP creates detailed specifications of UMTS technology. In order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created within the 3GPP for standardizing the UMTS by considering the independent nature of the network elements and their operations.
Each TSG develops, approves, and manages the standard specification within a related region. Among these groups, the radio access network (RAN) group (TSG-RAN) develops the standards for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
FIG. 1 illustrates an exemplary basic structure of a general UMTS network. As shown in FIG. 1, the UMTS is roughly divided into a terminal or user equipment (UE) 10, a UTRAN 20, and a core network (CN) 30.
The UTRAN 20 includes one or more radio network sub-systems (RNS) 25. Each RNS 25 includes a radio network controller (RNC) 23 and a plurality of Node-Bs (base stations) 21 managed by the RNC 23. The RNC 23 handles the assignment and management of radio resources and operates as an access point with respect to the core network 30.
The Node-Bs 21 receive information sent by the physical layer of the terminal 10 through an uplink and transmit data to the terminal 10 through a downlink. The Node-Bs 21 operate as access points of the UTRAN 20 for the terminal 10.
The UTRAN 20 constructs and maintains a radio access bearer (RAB) for communication between the terminal 10 and the core network 30. The core network 30 requests end-to-end quality of service (QoS) requirements from the RAB, and the RAB supports the QoS requirements the core network 30 has set. Accordingly, by constructing and maintaining the RAB, the UTRAN 20 can satisfy the end-to-end QoS requirements.
The services provided to a specific terminal 10 are roughly divided into the circuit switched (CS) services and the packet switched (PS) services. For example, a general voice conversation service is a circuit switched service, while a Web browsing service via an Internet connection is classified as a packet switched (PS) service.
For supporting circuit switched services, the RNCs 23 are connected to the mobile switching center (MSC) 31 of the core network 30 and the MSC 31 is connected to the gateway mobile switching center (GMSC) 33 that manages the connection with other networks. For supporting packet switched services, the RNCs 23 are connected to the serving general packet radio service (GPRS) support node (SGSN) 35 and the gateway GPRS support node (GGSN) 37 of the core network 30. The SGSN 35 supports the packet communications with the RNCs 23 and the GGSN 37 manages the connection with other packet switched networks, such as the Internet.
FIG. 2 illustrates a structure of a radio interface protocol between the terminal 10 and the UTRAN 20 according to the 3GPP radio access network standards. As shown in FIG. 2, the radio interface protocol has horizontal layers comprising a physical layer, a data link layer, and a network layer, and has vertical planes comprising a user plane (U-plane) for transmitting user data and a control plane (C-plane) for transmitting control information.
The user plane is a region that handles traffic information with the user, such as voice or Internet protocol (IP) packets. The control plane is a region that handles control information for an interface with a network, maintenance and management of a call, and the like.
The protocol layers in FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on the three lower layers of an open system interconnection (OSI) standard model.
The first layer (L1), namely, the physical layer, provides an information transfer service to an upper layer by using various radio transmission techniques. The physical layer is connected to an upper layer called a medium access control (MAC) layer, via a transport channel. The MAC layer and the physical layer exchange data via the transport channel.
The second layer (L2) includes a MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer, and a packet data convergence protocol (PDCP) layer.
The MAC layer handles mapping between logical channels and transport channels and provides allocation of the MAC parameters for allocation and re-allocation of radio resources. The MAC layer is connected to an upper layer called the radio link control (RLC) layer, via a logical channel.
Various logical channels are provided according to the type of information transmitted. In general, a control channel is used to transmit information of the control plane and a traffic channel is used to transmit information of the user plane.
A logical channel may be a common channel or a dedicated channel depending on whether the logical channel is shared. Logical channels include a dedicated traffic channel (DTCH), a dedicated control channel (DCCH), a common traffic channel (CTCH), a common control channel (CCCH), a broadcast control channel (BCCH), and a paging control channel (PCCH). The BCCH provides information including information utilized by a terminal 10 to access a system. The PCCH is used by the UTRAN 20 to access a terminal 10.
The MAC layer is connected to the physical layer by transport channels and can be divided into a MAC-b sub-layer, a MAC-d sub-layer, a MAC-c/sh sub-layer, and a MAC-hs sub-layer according to the type of transport channel being managed. The MAC-b sub-layer manages a BCH (Broadcast Channel), which is a transport channel handling the broadcasting of system information. The MAC-c/sh sub-layer manages a common transport channel, such as a forward access channel (FACH) or a downlink shared channel (DSCH), which is shared by a plurality of terminals. The MAC-d sub-layer manages a dedicated channel (DCH), which is a dedicated transport channel for a specific terminal 10. Accordingly, the MAC-d sublayer is located in a serving RNC (SRNC) that manages a corresponding terminal, and one MAC-d sublayer also exists in each terminal.
The RLC layer supports reliable data transmissions and performs segmentation and concatenation on a plurality of RLC service data units (SDUs) delivered from an upper layer. When the RLC layer receives the RLC SDUs from the upper layer, the RLC layer adjusts the size of each RLC SDU in an appropriate manner based upon processing capacity and then creates data units by adding header information thereto. The data units, called protocol data units (PDUs), are transferred to the MAC layer via a logical channel. The RLC layer includes a RLC buffer for storing the RLC SDUs and/or the RLC PDUs.
The BMC layer schedules a cell broadcast (CB) message transferred from the core network and broadcasts the CB message to terminals 10 positioned in a specific cell or cells.
The PDCP layer is located above the RLC layer. The PDCP layer is used to transmit network protocol data, such as the IPv4 or IPv6, effectively on a radio interface with a relatively small bandwidth. For this purpose, the PDCP layer reduces unnecessary control information used in a wired network, a function called header compression.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane. The RRC layer controls the transport channels and the physical channels in relation to setup, reconfiguration, and the release or cancellation of the radio bearers (RBs). The RB signifies a service provided by the second layer (L2) for data transmission between the terminal 10 and the UTRAN 20. In general, the set up of the RB refers to the process of stipulating the characteristics of a protocol layer and a channel required for providing a specific data service, and setting the respective detailed parameters and operation methods.
The RRC state refers to whether there exists a logical connection between the RRC of the terminal 10 and the RRC of the UTRAN 20. If there is a connection, the terminal 10 is said to be in RRC connected state. If there is no connection, the terminal 10 is said to be in idle state.
For terminals 10 in RRC connected state, because an RRC connection exists the UTRAN 20 can determine the existence of a particular terminal within the unit of cells, for example which cell the RRC connected state terminal is in. Thus, the terminal 10 can be effectively controlled.
In contrast, the UTRAN 20 cannot determine a terminal 10 in idle state. Such idle state terminals 10 can only be determined by the core network 30 to be within a region that is larger than a cell, namely, a location or a routing area. Therefore, the existence of idle state terminals 10 is determined within large regions, and, in order to receive mobile communication services such as voice or data, the idle state terminal must move or change into the RRC connected state.
When initially turned on by the user, a terminal 10 searches for an appropriate cell and then remains in idle state within the corresponding cell. When the idle state terminal 10 requires RRC connection, it transitions to the RRC connected state through an RRC connection procedure so that an RRC connection is made with the RRC layer of the UTRAN 20.
There are many situations where an idle state terminal 10 needs to establish an RRC connection. When uplink data transmission is necessary, for example when the user attempts to make a call, or when transmitting a response message in reply to a paging message received from the UTRAN 20, an idle state terminal 10 must establish an RRC connection. Another situation where an idle terminal 10 needs to establish an RRC connection is in order to receive a multimedia broadcast multicast service (MBMS).
The 3GPP system can provide multimedia broadcast multicast service (MBMS), which is a new type of service in Release 6. The 3GPP TSG SA (Service and System Aspect) defines various network elements and their functions required for supporting MBMS services. A cell broadcast service provided by the conventional Release 99 is limited to a service in which text type short messages are broadcast to a certain area. The MBMS service provided by Release 6 is a more advanced service that multicasts multimedia data to terminals (UEs) 10 that have subscribed to the corresponding service in addition to broadcasting multimedia data.
The MBMS service is a downward-dedicated service that provides a streaming or background service to a plurality of terminals 10 by using a common or dedicated downward channel. The MBMS service is divided into a broadcast mode and a multicast mode.
The MBMS broadcast mode facilitates transmitting multimedia data to every user located in a broadcast area, whereas the MBMS multicast mode facilitates transmitting multimedia data to a specific user group located in a multicast area. The broadcast area signifies a broadcast service available area and the multicast area signifies a multicast service available area.
Users who desire to receive the MBMS service first receive a service announcement provided by a network. The service announcement provides the terminal 10 with a list of services to be provided and related information. In addition, the users must receive a service notification provided by the network. The service notification provides the terminal 10 with information related to the broadcast data to be transmitted.
If the user intends to receive the multicast mode MBMS service, the user subscribes to a multicast subscription group. A multicast subscription group is a group of users who have completed a subscription procedure. Once a user has subscribed to the multicast subscription group, the user can join a multicast group to receive a specific multicast service. A multicast group is a group of users that receive a specific multicast service. Joining a multicast group, also referred to as MBMS multicast activation, means merging with the multicast group that has users who wish to receive the specific multicast service. Accordingly, the user can receive the specific multicast data by joining a multicast group, referred to as MBMS multicast activation.
The RNC 23 transfers the MBMS user data to the terminal 10 through the base station (Node-B) 21 via the user plane of the UTRAN protocol. The UTRAN 20 transfers the MBMS user data by constructing and maintaining a radio access bearer (RAB) for a call communication between the terminal 10 and the core network 30. The MBMS user data is transferred only by downlink. The MBMS radio bearer facilitates transferring, only to a specific terminal 10, the user data of a specific MBMS service transferred by the core network 30 to the UTRAN 20.
The MBMS radio bearer is divided into a point-to-multipoint type and a point-to-point type. The UTRAN 20 selects one of the two types of MBMS radio bearers to provide the MBMS service. To select one of the two MBMS radio bearers, the UTRAN 20 should recognize the number of users, or terminals 10, of a specific MBMS service existing in one cell.
The UTRAN 20 may count the number of terminals 10 to determine the type of MBMS radio bearer. The UTRAN 20 informs the terminals 10 that it is counting the number of terminals when it provides information about the MBMS service via a MBMS common control channel or performs paging for a specific MBMS service group.
When a terminal 10 receives a service notification of an MBMS service indicating that counting is being performed on the corresponding service, the terminal establishes a connection between an RRC entity of the terminal and an RRC entity of the UTRAN 20 by transferring an RRC connection request message to the UTRAN through an uplink common channel. The RRC connection request message informs the UTRAN 20 that the terminal 10 desires to receive the corresponding MBMS service.
By counting the number of terminals 10 that have transferred an RRC connection request message, the UTRAN 20 can recognize users who desire to receive the specific MBMS service in one cell. The UTRAN 20 then sets up an MBMS radio bearer on the basis of the count.
If the number of users, or terminals 10, existing in a corresponding cell is smaller than a certain threshold value, the UTRAN 20 sets a point-to-point MBMS radio bearer. If the number of users, or terminals 10, existing in a corresponding cell is greater than or equal to a certain threshold value, the UTRAN sets a point-to-multipoint MBMS radio bearer. However, the conventional paging method through which the UTRAN 20 recognizes the number of terminals 10 that desire to receive an MBMS service has shortcomings.
When the UTRAN 20 performs the MBMS service notification, response messages, such as RRC response messages, are transmitted from terminals 10 that desire to receive the MBMS service. The response messages are simultaneously concentrated at uplink channel, resulting in an increase in interference and load on the uplink. Because the UTRAN 20 performs the MBMS service notification to the plurality of terminals 10 using the MBMS common control channel and the corresponding terminals simultaneously inform the UTRAN that they want to receive the corresponding MBMS service through the uplink common channel both the interference and load on the uplink increases.
Because the interference and load increases, an undesirably long period of time may be required for the terminals 10 to send response messages. Therefore, some terminals may fail to transmit the response message by the time the UTRAN 20 should set up the MBMS radio bearer.
Once the UTRAN 20 receives a number of response messages from the terminals 10 that is above the threshold for setting up the MBMS point-to-multipoint radio bearer, the UTRAN no longer needs to receive additional response messages because all requirements for selecting the radio bearer have been met. However, in the conventional art, even if the UTRAN 20 has already received above a threshold number of response messages, the UTRAN continues to receive response messages until the MBMS radio bearer is set. Therefore, uplink radio resources are undesirably wasted.
The RRC connection procedure is generally divided into three steps; the terminal 10 transmits an kRC connection request message to the UTRAN 20, the UTRAN transmits an RRC connection setup message to the terminal, and the terminal transmits an RRC connection setup complete message to the UTRAN. These steps are illustrated in FIG. 3.
FIG. 3 illustrates the conventional art procedure when the UTRAN 20 accepts the RRC connection request of the terminal 10. When an idle state terminal 10 wishes to establish an RRC connection, the terminal first transmits an RRC connection request message to the UTRAN 20. The RRC connection request message may include an RRC establishment cause and an initial terminal identifier. The initial terminal identifier, or UE identity, is an identifier that is unique to a particular terminal 10 and allows that terminal to be identified despite its location anywhere in the world.
In response to the RRC connection request, the UTRAN 20 transmits an RRC connection setup message to the terminal 10. The RRC connection setup message may include an RNTI (Radio Network Temporary Identity) and radio bearer setup information transmitted together with an initial UE identity. The RNTI is a terminal identifier allocated to allow the UTRAN 20 to identify connected state terminals 10. The RNTI is used only when an RRC connection exists and is used only within the UTRAN 20.
In response to the RRC connection setup message, the terminal 10 establishes an RRC connection with the UTRAN 20 and transmits an RRC connection setup complete message to the UTRAN 20. After the RRC connection has been established, the terminal 10 uses the RNTI instead of the initial UE identity when communicating with the UTRAN 20.
Because the initial UE identity is a unique identifier, frequent use may increase the chances of undesirable exposure. Therefore, the initial UE identity is used briefly only during the initial RRC connection procedure and the RNTI is used thereafter for security reasons.
However, the UTRAN 20 may also reject the RRC connection request for a variety of reasons, for example insufficient radio resources. FIG. 4 illustrates the conventional art procedure when the UTRAN 20 rejects the RRC connection request of the terminal 10.
Upon receiving an RRC connection request from the terminal 10, the UTRAN 20 transmits an RRC connection reject message if it is necessary to reject the RRC connection. An initial UE identity and rejection cause are included in the RRC connection reject message to inform the terminal 10 why the RRC connection was rejected. Upon receiving the RRC connection reject message, the terminal 10 returns to an idle state.
FIG. 5 illustrates a conventional art method 100 for a terminal 10 requesting an RRC connection. The method 100 includes transmitting an RRC connection request message (S110) and operating a timer (S120), determining whether an RRC connection setup message (S130) or an RRC connection reject message (S144) is received before the timer expires (S150), and repeating the process unless an RRC connection setup message or an RRC connection reject message was received or it is determined that a threshold for sending RRC connection requests has been reached (S160).
Upon receiving an RRC connection request message from the terminal 10, the UTRAN 20 grants the RRC connection request if radio resources are sufficient and transmits an RRC connection setup message to the terminal. Otherwise the UTRAN rejects the RRC connection request and transmits an RRC connection reject message to the terminal 10.
Upon determining that an RRC connection setup message was received in step S130, the initial UE identity included in the RRC connection setup message is compared to the terminal's own identity to determine whether the message was intended for that terminal 10. If the initial UE identity included in the RRC connection setup message is different than that of the terminal 10, the terminal discards the received message and determines whether an RRC connection reject message was received in step S144. If the initial UE identity included in the RRC connection setup message matches that of the terminal 10, the terminal establishes an RRC connection with the UTRAN 20 and transitions to the RRC connected state.
Upon establishing an RRC connection with the UTRAN 20, the RNTI allocated by the UTRAN 20 is stored and an RRC connection setup complete message is transmitted to the UTRAN 20 in step S142. The RRC connection setup complete message includes capability information of the terminal 10. Transmission of additional RRC connection request messages is terminated in step S170.
Upon determining that an RRC connection reject message was received in step S144, the initial UE identity included in the RRC connection reject message is compared to the terminal's own identity to determine whether the message was intended for that terminal 10. If the initial UE identity included in the RRC connection reject message is different than that of the terminal 10, the terminal discards the received message and the state of the timer is checked in step S150. If the initial UE identity included in the RRC connection reject message matches that of the terminal 10, the terminal transitions to the idle state and terminates the RRC connection attempt in step S170.
Upon determining that the timer has not expired in step S150, the terminal 10 continues to wait for reception of an RRC connection setup message or an RRC connection reject message. Upon determining that the timer has expired in step S150, it is determined in step S160 if a threshold limit for sending RRC connection request messages has been reached.
If the threshold limit for sending RRC connection request messages has been reached, the terminal 10 terminates the RRC connection attempt in step S170. If the threshold limit for sending RRC connection request messages has not been reached, another RRC connection attempt is initiated in step S110 and the process is repeated.
In the conventional art, when the UTRAN 20 needs to send RRC connection reject messages to a plurality of terminals that requested RRC connection, radio resources are wasted because transmitting RRC connection reject messages requires an undesirably long time. A prime example of such wasted radio resources occurs when providing a multicast service.
The UTRAN 20 utilizes a multicast service notification procedure to perform a counting operation to determine the total number of terminals 10 wishing to receive a particular multicast service within a particular cell. The counting operation is used to determine whether the radio bearer to provide the particular multicast service should be point-to-multipoint or point-to-point. If the number of terminals existing in the corresponding cell is less than a threshold value, a point-to-point radio bearer is set. If the number of terminals is greater than or equal to the threshold, a point-to-multipoint radio bearer is set.
When a point-to-point radio bearer is set for a particular service, the terminals 10 wishing to receive the service are all in RRC connected state. However, when a point-to-multipoint radio bearer is set for a particular service, all terminals 10 wishing to receive the service need not be in RRC connected state because RRC idle state terminals are also able to receive the multicast service through the point-to-multipoint radio bearer.
For a multicast service, selecting the radio bearer type using the counting operation is essential for effectively allocating radio resources. Therefore, the selecting operation is performed before starting a multicast service or periodically during the multicast service.
In order to count the number of terminals 10 at the UTRAN 20, those terminals in idle state transmit an RRC connection request message to the UTRAN immediately upon receiving a service notification. When the UTRAN 20 receives an RRC connection request message after service notification, the number of terminals 10 wishing to receive a particular multicast service within a cell is counted to determine the type of radio bearer. Based on the radio resource conditions, RRC connection setup messages are transmitted to a certain number of terminals 10 and RRC connection reject messages are transmitted to the remaining terminals so that some terminals can receive the corresponding service in RRC idle state.
Because multicast service is a service aimed at a large number of terminals 10, the UTRAN 20 receives RRC connection request messages from a large number of terminals almost simultaneously after service notification. The UTRAN 20 typically rejects a majority of these RRC connection requests. Since each RRC connection reject message informs only one terminal 10 that its RRC connection request has been rejected, an extended period of time and large amount of radio resources are expended to transmit RRC connection reject messages to all corresponding terminals, particularly in a multicast service in which a very large number of terminals are handled.
Additionally, if a terminal 10 that transmitted an RRC connection request message does not receive an RRC connection setup message or an RRC connection reject message within a certain period of time, the terminal transmits the RRC connection request message again. The re-transmission of RRC connection request messages wastes further radio resources since the UTRAN must receive each re-transmitted message.
Therefore, there is a need for a method and apparatus that facilitates informing a plurality of terminals that their RRC connection request was rejected without having to send an RRC connection reject message to each terminal such that radio resources are conserved. The present invention addresses this and other needs.